1. Field
The following description relates to a Multiple Input Multiple Output (MIMO) communication system, and particularly, to a technique for adaptively updating or changing a codebook, and using the updated or changed codebook.
2. Description of Related Art
Currently, radio communication technologies have been developed to provide various multimedia services in a radio communication environment. However, a high transmission rate is required to provide multimedia services having a relatively high quality. Thus, various studies have been undertaken to support high transmission rates including the study of MIMO technology.
MIMO technology may increase a channel capacity with limited frequency resources by using multiple antennas. In theory, MIMO technology may use multiple antennas in an environment having superior scattering environment to provide a channel capacity in proportion to the number of antennas.
However, the space and area in which antennas are able to be installed may be limited for MIMO technology. In addition, intervals between the antennas may adversely affect a communication performance. Specifically, because space and area are limited, there may be a higher correlation between radio channels along with a reduction in the interval between the antennas. In particular, there is a significantly high correlation between the radio channels when the antennas have an identical polarization. Radio channels having the high correlation are not perfectly independent from each other. As a result, the high correlation may prevent the increase of a sum data rate of a communication system using MIMO technology. In addition, interference generated between the radio channels may decrease reliability and the transmission rate of data communication.
MIMO technology performs advanced coding of data, such as preceding to provide effective transmission of data. A scheme in which a rule for preceding data is expressed as a matrix is referred to as a preceding matrix. The preceding matrix may be generated based on at least one of the codeword matrices included in a codebook.
A base station may precode data based on channel state information about a channel between the base station and a mobile station and transmit the precoded data to the mobile station. The mobile station may estimate the channel state of the channel from the base station to the mobile station and feedback information about the estimated channel state to the base station. There are a limited number of bits of the feedback information, which is a constraint on transmitting accurate information about the channel.